Magneto-optic display device



\ I Oct. 8., 1963 H. w. FULLER ETAL 3,105,606

' MAGNETO-OPTIC DISPLAY DEVICE Filed July 19, 1961 2 Sheets-Sheet 1 E. HALE BY THOMAS L. McCQRMACK ATTORNEY 1963 H. w. FULLER ETAL 0 6 .MAGNETO-OPTIC DISPLAY DEVICE 2 Sheets-Sheet 2 Filed July 19, 1961 NLER EU m

V m M 'Y W W NH R FIG.4

United States Patent 3,106,606 MAGNETG-OPTIC DISPLAY DEVICE Harrison W. Fuller, Needham Heights, Mass, Murray E. Hale, Atkinson, N.H., and Thomas L. McCormack, Cheimsford, Mass, assignors to Laboratory For Electronics Inc., Boston, Mass., a corporation of Delaware Filed July 19, 1961, Ser. No. 125,258 15 Claims. (Cl. 178-6) The present invention relates in general to new and improved apparatus for displaying data and in particular to apparatus utilizing magneto optic effects in conjunction with magnetic media to display data.

In recent years great emphasis has been placed in the field of visual display devices to obtain display structures having the least possible dimension between the face of the display device and the rear of the package. In the field of cathode ray tubes this attempt has led to structures having extremely high voltages applied to the vertical and horizontal deflection plates (where the electron gun is positioned behind the face of the tube) or to structures having extremely stringent requirements placed on the voltages and dimensions (where the electron gun is positioned to one side and the beam is emitted parallel to the face and then bent in an arc to strike the front surface).

Further efforts have been made with varying degrees of success to provide electronic display devices which retain an image for a specified period of time. Many of these devices, however, are subject to eventual fading due to electrical leakage and temperature sensitivity. 0n the other hand devices which are not subject to these failings and which are able to retain images for an extended period of time are usually subject to the failing that erasure time is unduly long and frame frequency is fairly low. The most recent panel display devices use wire figures which, when energized, ionize a gas, or panel figures which are illuminated by light entering from the side. However, since both of these structures have no memory, the circuitry necessary to activate a particular image must be kept in use at all times while the image is being displayed.

Accordingly, it is the primary object of this invention to provide new and novel techniques for displaying data.

It is another object of this invention to provide improved display apparatus characterized by a minimal thickness and operative with small voltages and low power requirements.

It is a further object of this invention to provide improved apparatus for displaying, by use of magneto-optic effects, data written into a magnetic medium.

It is still another object of this invention to provide an improved display device which is able to hold an image indefinitely and still retain rapid frame frequency.

In the present invention polarized electromagnetic radiation is directed through a magnetic medium which has its magnetization vectors aligned initially in a preselected direction. A writing structure, when energized, rotates the direction of magnetization of localized portions of the magnetic medium in accordance with the data to be written and displayed. The polarized radiation emerging from each portion of the magnetic medium has its angle of polarization given a rotational increment or decrement depending upon the direction of magnetization of the particular portion of the magnetic medium traversed by the radiation. An analyzer, appropriately positioned, extinguishes radiation having one of the two resultant angles of polarization. The radiation passing the analyzer is directed, if necessary, upon a display screen and thereby gives a visual indication of the data present in the magnetic medium.

These and other features :of the invention together with further objects and advantages thereof will become apparent from the following detailed specification with reference to the accompanying drawings in which:

FIG. 1 illustrates the spatial relationships of the elements of a preferred embodiment of the apparatus according to the present invention utilizing the Faraday magneto-optic effect;

FIG. 2 represents a simplified and exploded view of the apparatus shown in FIG. 1 to illustrate the method in which the invention operates;

FIGS. 3a, 3b, and 3c illustrate several modifications of the writing structure and magnetic medium which have the advantages of allowing fast frame frequency and not requiring any erasure cycle;

FIG. 4 represents a simplified and exploded view of a modification of the apparatus shown in FIG. 1.

In the description which follows the magnetic medium may be a ferromagnetic material such as Fe, Ni, Co or alloys thereof, or MgBi and may be vacuum deposited onto a substrate. If the magnetic medium is composed of MgBi or a similar substance, the easy direction of magnetization and the magnetization vectors of the magnetic medium will be substantially normal to the plane of the medium; if it is composed of Fe, Ni, Co or alloys thereof, the easy direction of magnetization and the magnetization vectors of the magnetic medium will be substantially in the plane of the medium. In the latter instance where the magnetization vectors lie substantially in the plane of the medium, the impinging polarized radiation will have to strike the surface of the magnetic medium at an angle other than as the incremental or decremental rotation given to the angle of polarization by a magnetic medium is proportional to cos o (where o is the angle between the direction of incidence of the polarized radiation and the direction of the magnetization vectors of the medium).

In the description which follows, it is to be understood that the magnetic medium has its magnetization vectors initially aligned along its easy direction of magnetization.

The present invention is best illustrated with reference to FIG. 1. A panel source of electromagnetic radiation 10 emits radiation which passes through a polarizing medium 11, emerging therefrom with an angle of polariza tion 6. The polarized radiation then passes through a transparent wedge 12 which alters the direction of propagation of the polarized radiation, a writing structure 13, and an electrically insulating thin film 14. The polarized radiation then passes through a magnetic medium 15, having its magnetization vectors lying substantially in the plane of the medium, wherein the angle of polarization of each ray of the radiation is rotated by an amount $110, the sense of such rotation depending on the direction of magnetization of the portion of the magnetic medium 15 traversed by each ray of the polarized radiation. The emerging radiation, now normally composed of portions having an angle of polarization 0+A9 and 0A0, passes through a transparent wedge 16 which refracts the direction of propagation of the polarized radiation parallel to its original direction. The polarized radiation then enters an analyzing medium 17 which here has its angle of polarization fixed at The portion of the polarized radiation having an angle of polarization 6A0 is, therefore, extinguished while that portion having an angle of polarization 0+A0 is passed by the analyzing medium 17. The remaining polarized radiation is then amplified and visually displayed by an image intensifier and luminescent panel 18. The image intensifier and luminescent panel '18 may be combined in one unit as described in the I.R.E. Proceedings, vol. 28, page 1842, 1960. The writing structure 13, leads 30, and current source 31 will be further explained in reference to FIG. 2. A suitable enclosure 50 is provided to shield the device from the stray electric and/ or magnetic fields to complete the apparatus.

The magnetic medium may be vacuum deposited to any desired thickness as may be the insulating film. The polarizer and analyzer may be made of sheets of Polaroid made by the Polaroid Corporation or similar substances, while the radiation source and the image intensifier and luminescent screen are in the form of fiat thin panels. The wedges will preferably be composed of a substance which is substantially transparent to the radiation and which has a high index of refraction.

In FIG. 2 the method of operation of the invention is illustrated. A panel source of radiation 16 emits a beam of electromagnetic radiation 20 which, propagating in the Y direction, passes through a polarizer 11 and becomes the polarized beam 20a with an angle of polarization 0. The beam 20a then passes through a transparent wedge which increases in thickness in the -Z direction and alters the direction of propagation of the beam 20a to beam 20a as shown. The beam 20a then passes through a writing structure 13, shown here in the form of a figure '7," and impinges at an angle 90 on a magnetic medium 15 which here has its easy direction of magnetization in the Z direction.

The writing structure 13 is composed of a non-magnetic, electrically conductive material and is substantially transparent to the beam 20a. The writing structure 13, in this illustration, is vacuum deposited onto the magnetic medium 15 (the two elements being separated by medium 14, not shown in FIG. 2) so that its thickness in the Y" direction is small compared to its width. The magnetic field H which is created by current 1 generated by current source 31 and flowing through leads 30 and writing structure 13, lies substantially in the X-Z plane because of the large width to thickness ratio of the writing structure 13. Since the writing structure 13 acts to locally reverse the direction of magnetization of the magnetic medium 15 from the -Z to the +2 direction, as shown, the field H must be in the +Z" direction. This is accomplished by vacuum depositing the portion 13a (lying in the X direction) of the writing structure 13 in the form of a continuous fiat conductor. The portion of the writing structure 13 lying in the Z direction is deposited in the form of many flat, short sections 13b connected by wires 130. The current I then flows through the Writing structure 13 substantially in the +X direction and generates the magnetic field H in the +Z direction on the side of the writing structure 13 facing the magnetic medium 15. The field H when energized, reverses the direction of magnetization of a portion of the magnetic medium 15 giving a region 21 shown here in the shape of a figure 7.

The beam 20a passes through the magnetic medium 15 and emerges as beam 201; composed of portions having angles of polarization, 6+A0 and -A9, depending on the direction of magnetization of each portion of magnetic medium 15. The beam 2% then passes through the transparent wedge 16, shown as increasing in thickness in the +2 direction, and becomes beam 2012 parallel to beam 200. The analyzer 17 being set at an angle of polarization,

the beam 20c emerging therefrom consists only of those portions of beam 201) having an angle of polarization 0+A0. In this illustration, beam 20c will be in the form of the figure 7 of region 21 in the magnetic medium 15, and hence a figure 7 (not shown) will visually appear on the luminescent panel 18 as a light region on a dark background.

The magnetization vectors of the magnetic medium 15 having once been aligned along the easy direction of magnetization of the magnetic medium 15, will remain indefinitely in their state of alignment in the absence of any stray electric and/or magnetic fields, and hence the displayed figure will remain indefinitely until a change is desired. It is generally observed also that the magnetization vectors of an isotropic medium, i.e. one having no easy (or preferred) direction of magnetization, will remain oriented in the direction of an applied field even when the field is removed. Magnetic medium 15, in FIG. 2, could then be an isotropic medium which has been initially aligned by a transparent thin film conductor, as described below.

The displayed figure may be erased by pulsing a current through the writing structure 13 in a sense opposite to that of the current I used to establish the image. The figure could also be erased by placing a transparent thin film conductor, not shown, between the magnetic medium 15 and the wedge 16; if a current is now made to How through such conductor in the +X direction, an erasing field (or aligning field) would be generated in the Z direction.

It is evident that the image intensifier portion of element 18 is necessary only to improve contrast and/or raise the brightness level of the displayed figure when desired. If the radiation is visible light, it is obvious that the luminescent screen may not be necessary. The second transparent wedge is required only when one wishes to have the radiation normally incident upon the analyzer and the image intensifier and luminescent screen. If the displayed image is to be retained for extremely long periods of time, a high coercive force material should be used for the magnetic medium.

In certain applications it may be desired to make the angle much less than however, the thickness of the wedge 12 needed to retract the beam 20a onto the magnetic medium 15 at such an angle may become intolerably large. In such cases, the wedge 12 may be replaced by a bundle of fibers such as described in Fiber Optics, Scientific American, November 1960. The fibers would be properly curved to direct the beam 23a onto the magnetic medium 15 at the desired angle.

A method for obtaining fast frame frequency which does not require any erasure cycle is shown with reference to FIGS. 31:, 3b, and 30. In FIG. 3a, the magnetic medium 15 is shown having its easy direction of magnetization 25 at an angle of 45 with respect to the X and Z coordinate axes. The writing structure 13 is shown with elements 13a and 13b positioned parallel to the X and Z coordinate axes respectively. The current I (generated by means not shown in these figures) produces a magnetic field H lying substantially in the +Z direction; any fields produced by the wires 13c are negligible. The field H causes the magnetization vectors of the magnetic medium 15 to rotate out of the easy direction of magnetization 25 in the +2 direction. The magnetization vectors will remain in the +Z direction as long as the field H is applied. Polarized radiation (not shown) is incident upon the magnetic medium 15 at an angle 90 and emerges from the magnetic medium 15 composed of portions having either of two new angles of polarization. An analyzer, appropriately positioned, extinguishes radiation with one of the two new angles while allowing the remaining radiation to pass and be displayed. When the field H is removed, the magnetization vectors of the magnetic medium 15 return to their original alignment along the easy direction of magnetization 25.

In FIG. 3b a modification of the structure in FIG. 3a is illustrated. The conducting segments forming the writing structure 13 can be each individually energized (by any known means not shown). By energizing suitable combinations of the leads indicated by the numerals one through seven, any digit from zero to nine can be formed.

In FIG. 30 the writing structure 13 is shown as a matrix of fiat current carrying conductors energized by a plurality of leads, as leads 60 through 69 and leads 8% through 89. When a current is passed through any or all of the leads 60 through 69 a magnetic field H in the +2 direction is generated in the vicinity of the energized conductors; similarly a magnetic field H in the +X direction is generated by energizing leads 80 through 89. The fields H and H rotate the magnetization vectors of the magnetic medium out of the easy direction of magnetization 25, and, as described previously, polarized radiation passing through the regions so affected will pass through an analyzer set initially at extinction. If both fields H and H are applied simultaneously and are of equal magnitude, the resultant field is along the easy direction of magnetization and hence has no effect on the magnetization vectors of the magnetic medium 15. Furthermore the conductors can be deposited onto an insulating layer (not shown) on the magnetic medium 15 in such a manner that the magnetic fields H and H have an effect on the magnetic medium 15 only at the points of intersection of the conductors. This can easily be accomplished by changing the thickness of such an insulating layer between the points of intersection of the conductors. By well known coincident current techniques a variety of magnetic images may be produced in the magnetic medium 15. Some of these images may, however, have to be produced piecewise; the figure 7, for example, may be produced by first energizing leads 61 through 69 and 80 through 89, and then energizing leads 60 through 69 and through 88. If a broken image is permissible, leads 60 and 39 simultaneously energized will give the desired configuration. If it is desired to operate this structure so that the image is retained when the field H is not present, the direction of the magnetization vectors of the magnetic medium 15 should be rotated 180, and the sense of the energizing currents and the setting of the analyzer appropriately changed. The rotation of the magnetization vectors could be accomplished by the magnetic field of a thin film conductor, as previously described, or by a mechanical rotation of the magnetic medium itself.

It should be noted at this point that the fiat conductors need not be transparent to the radiation. The field generated by the conductors will affect the magnetization vectors of the magnetic medium over a region much larger than the physical dimensions of the conductors themselves. In addition, if the conductors are spaced sufficiently far from the magnetic medium, the incident radiation will be diffracted at the edges of the conductors and partially illuminate the region behind the conductors.

In FIG. 4 a simplified and exploded view of a modification of the apparatus of FIG. 1 is shown. The magnetic medium 15 consists of a magnetic material which has its easy direction of magnetization normal to the surface of the magnetic medium 15. It is obvious that the transparent wedges 12 and 16 of FIG. 2 are not necessary since the angle defined previously, is unequal to 90. The Writing structure 13 is modified from that shown in FIG. 2 to consist of a continuous conductor havingathickness comparable to its width. The magnetic field H generated by current 1.; now has a substantial component in -Y direction. The component in the Y direction reverses the direction of magnetization of a portion of the magnetic medium 15 to form a region 21 which has its magnetization vectors, as shown, in the Y direction.

It is advantageous to make the incremental rotation A6 as large as possible since the intensity of the radiation passing the analyzer is a cos function of the angle between the angle of polarization of the analyzer and the angle of the polarization of the radiation; the incremental rotation A6 it may be noted, is a function of the thickness and the specific rotation of the magnetic medium, as well as the angle defined above.

If a fiat package is not required, it is clear that the above apparatus may be modified to use the Kerr magnetooptic effect, whereby the necessary incremental rotation to the angle of polarization of the polarized radiation is provided by reflection from the magnetic medium. A simple and obvious rearrangement of the elements to position the analyzer and viewing screen on the same side of the magnetic medium as the source panel and polarizer will suifice.

It is not necessary for the analyzer to extinguish radiation with one angle of polarization so long as sufficient contrast can be obtained.

It is seen from the foregoing that this invention provides a fiat, thin display package in which, although the currents necessary to generate the magnetic fields may be large, the voltages and the power necessary are negligibly small. In addition the structure can be used either to have extremely rapid frame frequency or to hold the image indefinitely suitably rotating the magnetic medium and the analyzer.

Having thus described the invention, it will become apparent that numerous modifications and departures, as explained above, may now be made by those skilled in the art, and which fall within the scope of this invention. Consequently, the invention herein disclosed is to be construed as limited only by the spirit and scope of the appended claims.

What is claimed is:

1. Display apparatus comprising a magnetic medium, the magnetization vectors of said magnetic medium being initially aligned substantially parallel in a preselected direction; means for changing the magnetic orientation of a portion of said magnetization vectors of said magnetic medium to form a region of altered magnetic orientation in said magnetic medium in accordance with data to be displayed, said means including a non-magnetic electrically conductive writing structure; means for irradiating one entire surface of said magnetic medium with polarized electromagnetic radiation, at least a portion of said electromagnetic radiation intercepting said magnetization vectors of said magnetic medium at an angle less than and means for visually displaying radiation emer ing from said magnetic medium with a preselected angle of polarization in accordance with said data in said magnetic medium.

2. The apparatus of claim 1 wherein said writing structure comprises a matrix of crossed non-magnetic conductors disposed parallel to and in close proximity with said magnetic medium.

3. The apparatus of claim 1 wherein said writing structure comprises a continuous non-magnetic conductor having the spatial shape of the data to be displayed and disposed parallel to and in close proximity with said magnetic medium.

4. The apparatus of claim 1 wherein said writing structure comprises a plurality of non-overlapping non-magnetic conductors disposed parallel to and in close proximity with said magnetic medium, individual ones of said conductors being spatially arranged so that different combinations thereof are representative of the data to be displayed.

5. Display apparatus comprising a thin film magnetic medium having an easy direction of magnetization substantially parallel to the surface of said magnetic medium, the magnetization vectors of said magnetic medium being initially aligned substantially parallel to said easy direction of magnetization; means for changing the orientation of a portion of said magnetization vectors of said magnetic medium in accordance with data to be displayed, said means including a non-magnetic, electrically conductive writing structure to produce a magnetic field substantially parallel to said surface of said magnetic medium; a source of electromagnetic radiation and a polarizing medium disposed parallel and in close proximity thereto; means for directing the polarized radiation emerging from said polarizer upon said magnetic medium at an angle less than 90; an analyzing medium positioned to receive polarized electromagnetic radiation emerging from said magnetic medium and adapted to pass electromagnetic radiation emerging with a preselected angle of polarization therefrom, said polarized electromagnetic radiation passing said analyzer being representative of the data in said magnetic medium; and means for visually displaying said electromagnetic radiation passing said analyzer.

6. The apparatus of claim wherein said means for directing the polarized radiation consists of a wedge sub stantially transparent to the polarized radiation.

7. The apparatus of claim 5 wherein said means for directing the polarized radiation consists of a bundle of fibers to direct said polarized radiation onto said magnetic medium.

8. The apparatus of claim 5 and, in addition, means for aligning said magnetization vectors substantially parallel to said easy direction of magnetization, said means including a substantially transparent thin film non-magnetic electrically conducting medium disposed parallel to and in close proximity with said magnetic medium and on the opposite side of said magnetic medium from said writing structure.

9. The apparatus of claim 5 wherein said writing structure comprises a matrix of crossed nonmagnetic conductors, the elements of said matrix having a large width to thickness ratio.

10. The apparatus of claim 5 wherein said writing structure comprises a first and a second plurality of discontinuous non-magnetic conductors, said first plurality of conductors being in the form of fiat parallel strips, said second plurality of conductors being normal to said first plurality and each one of said second plurality being in the form of discontinuous fiat segments connected by Wires, all said elements disposed parallel to and in close proximity with said magnetic medium, and means for selectively energizing each one of the conductors in said first and said second plurality of conductors.

11. The apparatus of claim 5 wherein said writing means reverses the magnetic orientation of a portion of said magnetization vectors.

12. Display apparatus comprising a thin film magnetic medium having an easy direction of magnetization substantially normal to the surface of said magnetic medium, the magnetization vectors of said magnetic medium being initially aligned substantially parallel to said easy direction of magnetization; writing means for reversing the orientation of at least a portion of said magnetization vectors of said magnetic medium in accordance with data to be displayed, said means including a non-magnetic, electrically conductive writing structure to produce a magnetic field substantially normal to said surface of said magnetic medium; a source of electromagnetic radiation and a polarizing medium adapted to irradiate said magnetic medium with polarized electromagnetic radiation; an analyzing medium positioned to receive polarized electromagnetic radiation emerging from said magnetic medium and adapted to pass electromagnetic radiation emerging from said magnetic medium with a preselected angle of polarization, said polarized electromagnetic radiation passing said analyzer being representative of the data in said magnetic medium; and means for visually displaying said electromagnetic radiation passing said analyzer.

13. The apparatus of claim 12 wherein the Width to thickness ratio of any element of said non-magnetic, electrically conductive writing structure is substantially unity.

14-. Display apparatus in which an image is first written into a magnetic medium as a region of altered magnetic orientation by a non-magnetic, electrically conductive Writing structure and then is visually displayed by directing polarized electromagnetic radiation through the magnetic medium and allowing the radiation emerging from the magnetic medium with a preselected angle of polarization to fall upon a luminescent panel comprising: a panel source of electromagnetic radiation; a thin film polarizing medium; a thin film writing structure; means for energizing said writing structure; a thin film magnetic medium; a thin film analyzing medium; and an electromagnetic radiation responsive luminescent panel, all said elements being substantially parallel and sequentially disposed in close proximity with one another.

15. The apparatus of claim 14 and, in addition, means for mechanically rotating said magnetic medium with respect to said Writing structure.

References Cited in the file of this patent 

1. DISPLAY APPARATUS COMPRISING A MAGNETIC MEDIUM, THE MAGNETIZATION VECTORS OF SAID MAGNETIC MEDIUM BEING INITIALLY ALIGNED SUBSTANTIALLY PARALLEL IN A PRESELECTED DIRECTION; MEANS FOR CHANGING THE MAGNETIC ORIENTATION OF A PORTION OF SAID MAGNETIZATION VECTORS OF SAID MAGNETIC MEDIUM TO FORM A REGION OF ALTERED MAGNETIC ORIENTATION IN SAID MAGNETIC MEDIUM IN ACCORDANCE WITH DATA TO BE DISPLAYED, SAID MEANS INCLUDING A NON-MAGNETIC ELECTRICALLY CONDUCTIVE WRITING STRUCTURE; MEANS FOR IRRADIATING ONE ENTIRE SURFACE OF SAID MAGNETIC MEDIUM WITH POLARIZED ELECTROMAGNETIC RADIATION, AT LEAST A PORTION OF SAID ELECTROMAGNETIC RADIATION INTERCEPTING SAID MAGNETIZATION VECTORS OF SAID MAGNETIC MEDIUM AT AN ANGLE LESS THAN 90*; AND MEANS FOR VISUALLY DISPLAYING 